Field of the Invention
At least one embodiment in accordance with the present invention relates generally to control of an uninterruptable power supply input circuit.
Discussion of Related Art
Power converters may be employed to convert a multiphase AC input to a DC output. The DC output is often supplied to a DC bus or link. For example, an uninterruptible power supply (“UPS”) may include a power converter and may further include an inverter, which converts the DC power supplied by the DC bus to an AC signal at an output of the UPS. The DC bus may connect the output of the power converter to an input of the inverter. The UPS may also include a backup source of DC power (e.g., a battery power source, a DC generator, etc.). The output of the UPS can be connected to an electrical load to increase the reliability of the power supplied to the load.
Various types of UPS systems may employ power converters. For example, power converters may be employed in an on-line UPS that can supply power derived from a primary source of power and/or a backup source of power without interruption provided either the primary power source or the secondary power source is available. Power converters may also be employed in an off-line UPS system that includes a transfer switch that switches power if primary power is lost unexpectedly and there is an interruption in power supplied to the electrical load.
The average power obtained from an AC line supply through the UPS described above is typically less than the product of the RMS (root mean square) voltage and the RMS current. The ratio of the average power to the product of the RMS voltage and the RMS current is known as the power factor. Power Factor Correction (PFC) is used to improve an input power factor and comply with various utility standards. Some utilities add additional charges or penalize customers having equipment that does not include PFC. PFC schemes control the input current drawn by a UPS to follow the input voltage in both shape and time.